Technique for increasing adhesion of metallization layers by providing dummy vias

ABSTRACT

By providing dummy vias below electrically non-functional metal regions, the risk for metal delamination in subsequent processes may be significantly reduced. Moreover, in some embodiments, the mechanical strength of the resulting metallization layers may be even more enhanced by providing dummy metal regions, which may act as anchors for an overlying non-functional metal region. In addition, dummy vias may also be provided in combination with electrically functional metal lines and regions, thereby also enhancing the mechanical stability and the electrical performance thereof.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Generally, the present invention relates to the formation of integratedcircuits, and, more particularly, to the formation of metallizationlayers including highly conductive metals, such as copper, embedded intoa dielectric material.

2. Description of the Related Art

In an integrated circuit, a very large number of circuit elements, suchas transistors, capacitors, resistors and the like, are formed in or onan appropriate substrate, usually in a substantially planarconfiguration. Due to the large number of circuit elements and therequired complex layout of advanced integrated circuits, the electricalconnections of the individual circuit elements are generally notestablished within the same level on which the circuit elements aremanufactured. Typically, such electrical connections are formed in oneor more additional “wiring” layers, also referred to as metallizationlayers. These metallization layers generally include metal-containinglines, providing the inner-level electrical connection, and also includea plurality of inter-level connections, also referred to as vias, filledwith an appropriate metal. The vias provide electrical connectionbetween two neighboring stacked metallization layers, wherein themetal-containing lines and vias may also be commonly referred to asinterconnect structures.

Due to the continuous shrinkage of the feature sizes of circuit elementsin modern integrated circuits, the number of circuit elements for agiven chip area, that is the packing density, also increases, therebyrequiring an even larger increase in the number of electricalinterconnections to provide the desired circuit functionality.Therefore, the number of stacked metallization layers may increase andthe dimensions of the individual lines and vias may be reduced as thenumber of circuit elements per chip area becomes larger. The fabricationof a plurality of metallization layers entails extremely challengingissues to be solved, such as mechanical, thermal and electricalreliability of a plurality of stacked layers. As the complexity ofintegrated circuits advances and brings about the necessity forconductive lines that can withstand moderately high current densities,semiconductor manufacturers are increasingly replacing the well-knownmetallization metal aluminum with a metal that allows higher currentdensities and hence allows a reduction in the dimensions of theinterconnections and thus the number of stacked metallization layers.For example, copper and alloys thereof are materials that areincreasingly used to replace aluminum due to their superiorcharacteristics in view of higher resistance against electromigrationand significantly lower electrical resistivity when compared withaluminum. Despite these advantages, copper and copper alloys alsoexhibit a number of disadvantages regarding the processing and handlingin a semiconductor facility. For instance, copper may not be efficientlyapplied onto a substrate in larger amounts by well-establisheddeposition methods, such as chemical vapor deposition (CVD), and alsomay not be effectively patterned by the usually employed anisotropicetch procedures. Consequently, in manufacturing metallization layersincluding copper, the so-called inlaid or damascene technique (singleand dual) is preferably used, wherein a dielectric layer is firstapplied and then patterned to receive trenches and/or vias, which aresubsequently filled with copper or copper alloys.

It turns out that the process of forming vias and trenches in thedielectric material of the respective metallization layer according tothe damascene regime may significantly affect the overall productionyield during the formation of advanced semiconductor devices havingcopper-based metallization layers owing to delamination issues andetch-related geometry effects.

With reference to FIGS. 1 a-1 d, a typical conventional process flowwill now be described in more detail so as to more clearly demonstratethe problems involved in forming highly scaled metal lines in adielectric material according to a damascene process, for instance, adual damascene process, in which vias are formed prior to correspondingtrenches connected to the vias, wherein this approach is often called a“via first/trench last” approach.

FIG. 1 a schematically shows a cross-sectional view of a semiconductordevice 100 comprising a substrate 101, which may be provided in the formof a bulk silicon substrate, a silicon-on-insulator (SOI) substrate andthe like, wherein the substrate 101 may also represent a device layerhaving formed therein individual circuit elements, such as transistors,capacitors, lines, resistors, contact portions and the like. Forconvenience, any such circuit elements are not shown in FIG. 1 a. Thedevice 100 comprises a first device region 120A and a second deviceregion 120B, wherein the first device region 120A may represent an“inner” region that receives metal lines and vias, whereas the seconddevice region 120B may represent a device region for receiving a largemetal area in the respective metallization layer together withcorresponding metal lines in the first device region 120A. For example,a measurement region and the like may be formed in the second deviceregion 120B, as is typically provided for evaluating so-called dishingeffects occurring during the removal of excess copper by chemicalmechanical polishing (CMP).

The device 100 further comprises a dielectric layer 102 formed above thesubstrate 101, wherein the layer 102 may represent a dielectric materialenclosing the individual circuit elements, also referred to as a contactmaterial, or the layer 102 may represent a portion of a lower-lyingmetallization layer, in which any metal-filled lines may be embedded.Depending on the specific design of the device 100, or the function ofthe layer 102, it may be comprised of a conventional dielectric materialsuch as silicon dioxide, silicon nitride, or it may comprise a low-kdielectric material such as, for instance, hydrogen-enriched siliconoxycarbide (SiCOH) and the like. A metal line 103A is formed within thefirst device region 120A and above the substrate 101 and at leastpartially within the layer 102 for establishing an electric connectionto circuit elements formed within the first device region 120A. Themetal line 103A may be comprised of a copper-containing metal includingconductive barrier layers (not shown) so as to enhance adhesion of themetal line 103A to the surrounding material and reduce diffusion ofcopper into sensitive device regions. An etch stop layer 104 is formedon the dielectric layer 102 and the metal line 103A, wherein the etchstop layer 104 may be comprised of a material that exhibits a high etchselectivity to the material of a dielectric layer 105 formed on the etchstop layer 104. Furthermore, the etch stop layer 104 may also act as adiffusion barrier between the metal line 103A and neighboring materialsto reduce the out-diffusion of metal, such as copper, and diffusion ofdielectric material into the metal line 103A.

The dielectric layer 105, which may be comprised of a low-k dielectricmaterial, is formed on the etch stop layer 104, followed by ananti-reflective coating (ARC) layer or capping layer 106, which may beformed from two or more sub-layers so as to achieve the desiredperformance with respect to the optical behavior, mechanical strengthand masking characteristics. For instance, the capping layer 106 may beprovided as a stack including a silicon dioxide layer (acting to impartimproved mechanical strength to the layer 105 when formed of a low-kmaterial), a silicon oxynitride layer for adapting the optical behaviorand a thin silicon dioxide layer acting as a nitrogen barrier for aresist mask 107 formed on the capping layer 106. The resist mask 107includes a first opening 107A above the first device region 120A thatcorresponds to a via opening 105A for electrically connecting the metalline 103A with a metal line still to be formed in the dielectric layer105.

A typical process flow for forming the semiconductor device 100 as shownin FIG. 1 a may comprise the following processes. After the fabricationof any circuit elements within the substrate 101, the dielectric layer102 may be deposited by well-established deposition recipes based onplasma enhanced chemical vapor deposition (PECVD). For example, thelayer 102 may be comprised of silicon dioxide, fluorine-doped silicondioxide or SiCOH and hence deposition recipes on the basis ofappropriate precursors may be employed to form the layer 102. Then, themetal line 103A may be formed in accordance with processes as will bedescribed in the following with reference to the layer 105. Thereafter,the etch stop layer 104 is deposited by, for instance, well-establishedPECVD techniques with a thickness that is sufficient to reliably stop avia and trench etch process to be performed later on. Next, thedielectric layer 105 is formed by CVD or spin-coating, depending on thematerial used. Then, the capping layer 106 is formed by PECVD techniqueson the basis of well-established recipes to provide the desiredcharacteristics in the further processing of the device 100. Finally,the resist mask 107 may be formed by advanced photolithography to formthe respective opening 107A. Thereafter, an anisotropic etch process isperformed, wherein, in an initial phase, the exposed portion of thelayer 106 is removed and, in a subsequent process, the dielectricmaterial of the layer 105 is removed to form the via opening 105A.

FIG. 1 b schematically illustrates the device 100 in an advancedmanufacturing stage. The device 100 now comprises a resist mask 109having formed therein a trench 109A above the via opening 105A withdimensions corresponding to design dimensions of a metal line to beformed above and around the via opening 105A. The resist mask 109further comprises an opening 109B in the second device region 120Bformed in accordance with the design dimensions for a correspondingmetal region, such as a test region, wherein the dimensions of theopening 109B may be significantly greater compared to the dimension ofthe trench 109A, at least in one dimension. For instance, the opening109B may have a design dimension of 100 μm×100 μm in advancedsemiconductor devices of minimal critical dimensions of 50 nm or evenless. Moreover, a fill material 108 is formed underneath the resist mask109, wherein the fill material 108 is also provided within the opening105A. The fill material may be comprised of a photoresist of differenttype compared to the resist mask 109, or the fill material 108 mayrepresent any other polymer material that may be applied in a lowviscous state to fill the opening 105A while providing a substantiallyplanar surface. The fill material 108 may also serve as an ARC layerduring the patterning of the resist mask 109.

The resist mask 109 may be formed by first applying the fill material108 by, for example, spin-coating a resist or a polymer material, thenapplying a photoresist by spin-coating, performing a well-establishedphotolithography process and etching or dry-developing the fill material108 on the basis of the resist mask 109. Thereafter, the device 100 issubjected to an etch ambient 110 on the basis of carbon and fluorine toetch through the layer 106 and remove a portion of the layer 105 to forma trench around the via opening 105A and an opening in the second deviceregion 120B corresponding to the opening 109B, while the fill material108 in the via opening 105A prevents substantial material removaltherein. Moreover, the fill material 108 within the opening 105A,although partially removed during the etch process 110, protects theremaining etch stop layer 104 in the opening 105A so that the metal line103A is not exposed to the etch ambient 110. Thereafter, a trench ofspecified depth is formed around the via opening 105A and acorresponding opening in the second device region 120B, the resist mask109 and the fill material 108 are removed by, for instance, anoxygen-based plasma treatment.

During the etch process 110, the removal rate for material of thedielectric layer 105 may significantly depend on the geometric structureof the trenches and openings to be formed in the dielectric layer 105.For example, the etch rate at the trench opening 109A, when for instancerepresenting an isolated trench, may be significantly higher compared tothe rate at the opening 109B designed to represent a test region.Generally, in modern semiconductor devices, substantially continuousnon-tiled metal plates of increased dimensions compared to metal linesin product areas may be required for a variety of test and measurementtasks. Consequently, due to the structure and geometry dependent etchbehavior, the etch depth and thus the finally achieved thickness of thelarge-area metal regions may be reduced compared to actual metal lines,thereby potentially resulting in an overall reduced stability of therespective metallization layer.

FIG. 1 c schematically shows the device after the above process sequencewith a trench 111A and an opening 111B formed in the layer 106 and thedielectric layer 105 in the first and second device regions 120A and120B, respectively. Moreover the device is subjected to a further etchprocess 112 to remove the remaining etch stop layer 104 to therebyconnect the via opening 105A to the metal region 103. The via opening105A, the trench 111A and the opening 111B may then be filled withmetal, such as copper or copper alloys, by electrochemical depositiontechniques, wherein, prior to the electrochemical deposition,corresponding barrier and seed layers may be formed.

FIG. 1 d schematically depicts the device 100 after completion of theabove-described process sequence. Thus, the device 100 comprises ametal-filled via 113A connecting to the metal region 103 and a metalline 112A formed above the via 113A. In the second device region 120B, ametal area 112B is formed, whose thickness may be reduced compared tothe thickness of the metal line 112A due to potential etchnon-uniformities during the etch process 110, as previously explained.Moreover, the metal area 112B may exhibit a reduced adhesion to theadjacent dielectric material of the layer 105, which may causedelamination of metal during manufacturing processes after the metaldeposition, such as CMP and the like, during which increased mechanicalstress may be applied to the device 100. Consequently, production yieldmay be compromised and device performance reduced.

In view of the situation described above, there exists a need for animproved technique which solves or at least reduces the effects of oneor more of the problems identified above.

SUMMARY OF THE INVENTION

The following presents a simplified summary of the invention in order toprovide a basic understanding of some aspects of the invention. Thissummary is not an exhaustive overview of the invention. It is notintended to identify key or critical elements of the invention or todelineate the scope of the invention. Its sole purpose is to presentsome concepts in a simplified form as a prelude to the more detaileddescription that is discussed later.

Generally, the present invention is directed to a technique that enablesthe formation of metallization layers of semiconductor devices includinglarge-area metal regions with enhanced stability in that the large-areametal region is formed above at least some dummy vias connected thereto,thereby increasing the adhesion to the surrounding dielectric materialand potentially reducing etch non-uniformities during the formation ofrespective openings within the dielectric materials. A dummy via may beunderstood as a metal-filled plug extending at least partially throughthe dielectric material towards a lower-lying material layer, whereinthe dummy via, in contrast to functional vias provided in product areasof a semiconductor device, may not be electrically connected to anysemiconductor circuit elements that are required for a specified circuitlayout of an integrated circuit to be operational. By providingadditional dummy vias, the effective adhesion area with respect to theneighboring dielectric material of an overlaying metal region may besignificantly increased, which may reduce the probability for theoccurrence of metal delamination and other defect mechanisms during theformation of metallization layers in advanced semiconductor devices.

According to one illustrative embodiment of the present invention, amethod comprises identifying a region of reduced via density in ametallization layer of a semiconductor device and forming a dummy via inthe identified region. Moreover, the method comprises forming a metalregion above the identified region, wherein the metal region isconnected to the dummy via.

According to another illustrative embodiment of the present invention, amethod comprises forming a plurality of vias in a first portion of afirst dielectric layer of a semiconductor device, wherein at least someof the plurality of vias are electrically non-functional vias.Furthermore, the method comprises forming a first metal region in asecond portion of the first dielectric layer, wherein the second portionis located above the first portion and the first metal region isconnected to at least one of the electrically non-functional vias.

According to yet another illustrative embodiment of the presentinvention, a semiconductor device comprises one or more semiconductorcircuit elements formed above the substrate and a metallization layerformed above the one or more semiconductor circuit elements. Themetallization layer comprises a first metal region and one or more dummyvias located below the first metal region, wherein one end of the one ormore dummy vias is connected to the first metal region, while the otherend remains insulated from the one or more semiconductor circuitelements.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be understood by reference to the followingdescription taken in conjunction with the accompanying drawings, inwhich like reference numerals identify like elements, and in which:

FIGS. 1 a-1 d schematically show cross-sectional views of asemiconductor device during the formation of a metallization layerincluding metal lines and a large-area metal region for test purposesduring various manufacturing stages in accordance with a conventionalprocess technique;

FIGS. 2 a-2 b schematically show a top view and a cross-sectional view,respectively, of a semiconductor device in the form of a design layout,which may be used for identifying areas in a metallization layer havinga reduced via density;

FIG. 2 c schematically shows a top view of a semiconductor devicecomprising a plurality of dummy vias within a specified metallizationlayer in an area that has previously been identified as having a reducedvia density;

FIGS. 2 d-2 e schematically illustrate cross-sectional views of asemiconductor device having formed therein a plurality of dummy vias;and

FIG. 3 schematically illustrates a cross-sectional view of asemiconductor device including a large-area metal region formed above aplurality of dummy vias, which in turn are connected to a dummy metalregion in a lower-lying metallization layer.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and are herein described in detail. It shouldbe understood, however, that the description herein of specificembodiments is not intended to limit the invention to the particularforms disclosed, but on the contrary, the intention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure.

The present invention will now be described with reference to theattached figures. Various structures, systems and devices areschematically depicted in the drawings for purposes of explanation onlyand so as to not obscure the present invention with details that arewell known to those skilled in the art. Nevertheless, the attacheddrawings are included to describe and explain illustrative examples ofthe present invention. The words and phrases used herein should beunderstood and interpreted to have a meaning consistent with theunderstanding of those words and phrases by those skilled in therelevant art. No special definition of a term or phrase, i.e., adefinition that is different from the ordinary and customary meaning asunderstood by those skilled in the art, is intended to be implied byconsistent usage of the term or phrase herein. To the extent that a termor phrase is intended to have a special meaning, i.e., a meaning otherthan that understood by skilled artisans, such a special definition willbe expressly set forth in the specification in a definitional mannerthat directly and unequivocally provides the special definition for theterm or phrase.

The present invention is generally directed to a technique for formingmetallization layers in accordance with a damascene or inlaid strategy,wherein, in addition to metal lines and vias, large-area metal regionsare also provided. In this respect, a metallization layer is to beunderstood as a dielectric layer formed above a device layer, i.e., oneor more layers having formed therein semiconductor circuit elements,such as transistors, capacitors, resistors and the like, wherein metallines and metal regions are provided in the dielectric material, whichprovide the inner layer electrical connection of circuit elements,whereas vias may be connected at certain locations to the respectivemetal lines to establish an electrical connection to a lower-lying metalregion, thereby finally providing an electrical connection to one ormore of the semiconductor circuit elements within the device layer.

As previously explained, in highly sophisticated semiconductor devices,highly conductive metals, such as copper and copper alloys, aretypically used which may be formed on the basis of the damascenetechnique, in which the dielectric material is provided with respectiveopenings that are subsequently filled with the copper or copper alloy,thereby requiring advanced anisotropic etch techniques. Moreover, copperand alloys thereof are frequently used in combination with low-kdielectric materials, i.e., materials having a dielectric constant of3.0 or even less, which may exhibit a reduced adhesion to the filled-inmetal. Consequently, an increased probability for metal delaminationfrom the surrounding dielectric material may be observed, in particular,when metal regions of increased lateral dimensions are to be formed in aspecified metallization layer. For example, in some metallization layersof a metallization stack, metal regions may be provided for testpurposes which may have no electrical connection to a lower-lying metalor contact region. Due to the reduced adhesion to the surroundingdielectric material, particularly if a low-k dielectric material isconsidered, a high risk of metal delamination may exist in subsequentprocess steps, such as CMP, and/or the metal thickness may varysignificantly within a metallization layer, or from layer to layer, dueto a significant non-uniformity of the geometric structure of ametallization layer, which may include a plurality of metal lines havingdesign dimensions in accordance with the design rules, while metalregions with significantly increased lateral dimensions compared to theregular metal lines are also provided. For example, in advancedsemiconductor devices, a width of a metal line in a lower metallizationlayer may be in the range of 1 μm or even less, while, on the otherhand, large-area metal regions are included having lateral dimensionsof, for instance, 80 μm×80 μm so that at least one lateral dimension issignificantly larger compared to the width of the regular metal lines.

Without intending to restrict the present invention to the followingexplanation, it is believed that a significant non-uniformity during theanisotropic etch process for forming respective openings for metal linesand other metal regions is caused or influenced by the geometricdifference in dimensions and shape, resulting in a reduced etch depth oflarge-area openings that are formed above a substantially via-free area.For example, recent investigations performed by the inventors seem toindicate that a metal region formed above a dense via area is thickerthan a metal region formed above an area without vias or with asignificantly reduced via density. Consequently, the present inventioncontemplates the introduction of additional dummy vias, i.e., vias thatare not required for the electrical functionality of the semiconductordevice under consideration, so as to reduce process non-uniformitiesduring the formation of metal lines and large-area metal regions,wherein the additional dummy vias significantly enhance the overalladhesion surface area that is provided for the overlying metal region,thereby significantly enhancing the overall adhesion to the surroundingdielectric material.

With reference to FIGS. 2 a-2 e and 3, further illustrative embodimentsof the present invention will now be described in more detail. FIG. 2 aschematically illustrates a top view of a semiconductor device 200,wherein FIG. 2 a may be understood as representing a circuit layout ofan integrated circuit that may be included in the semiconductor device200. In other cases, the semiconductor device 200 may be understood asrepresenting a certain type of semiconductor device including all thefunctional and non-functional components as required for the fabricationof a specific type of semiconductor device. For instance, thesemiconductor device 200 may represent the layout or a real version of asemiconductor device similar to that shown in FIGS. 1 a-1 b, in whichareas of reduced via density in a specific metallization layer may belocated and identified. Hence, the semiconductor device 200 or thelayout thereof may comprise one or more metallization layers, one ofwhich is indicated in the top view of FIG. 2 a by reference number 230.The device 200 may comprise at least a first device region 220A and asecond device region 220B, which may not necessarily be located in thesame die region, when the second device region 220B is to represent aspecified test region that has to be provided at a few specifiedsubstrate locations only. In other illustrative embodiments, the firstand second device regions 220A and 220B may be located within the samedie region, i.e., within a portion formed above an appropriatesubstrate, which may act as a functional unit after dicing the substrateand separating the individual die regions. The first device region 220Amay include a plurality of metal lines 212A, 212C, 212D that may beconnected by respective vias 213A to any lower-lying contact regions ormetal regions. It should be appreciated that the metal lines 212A, 212C,212D of the metallization layer 230 formed in the first device region220A may have substantially the same configuration or may differ insize, depending on the design requirements. By way of example, one ofthe exemplary metal lines, i.e., the line 212A, may have a greater widthcompared to the metal lines 212C, 212D. Moreover, the vias 213A areshown to have substantially the same design dimensions, whereas, inother illustrative embodiments, respective vias may have differentdimensions.

In the second device region 220B, a metal region 212B may be provided,which may exhibit significantly increased dimensions, at least in onelateral direction, wherein an area corresponding to the metal region212B may have a significantly reduced via density compared to thecorresponding metal-containing regions represented by the metal lines212A, 212C and 212D. It should be appreciated that the term “viadensity” is to be understood as the number or the area of vias formedbelow a respective metal region and being connected thereto. In otherwords, a via density may be understood as the ratio of the total areaoccupied by the vias 213A with respect to the total area of acorresponding metal region, such as the metal line 212A. For example,the via density of the area corresponding to the metal region 212B maybe zero, since in this stage of design or manufacture no vias areprovided for the metal region 212B, since no electrical connection isrequired to any lower-lying circuit elements. On the other hand, themetal line 212A may exhibit a moderately high via density, depending onthe total area of the metal line 212A and the size and number of vias213A connected thereto.

FIG. 2 b schematically shows a cross-sectional view of the layout of thedevice 200, wherein the cross-section is taken along the line indicatedin FIG. 2 a as IIb. Hence, the device 200 or its layout may comprise asubstrate 201 in and on which is provided a device layer 240, which mayinclude a plurality of circuit elements, such as semiconductor circuitelements in the form of transistors, resistors, capacitors and the like.The corresponding circuit elements are collectively indicated as 241,which may represent, in the illustrative embodiment depicted in FIG. 2b, a field effect transistor, wherein the cross-section is taken alongthe transistor width direction, that is, the horizontal direction inFIG. 2 b may represent the width direction of the transistor 241.Moreover, the device layer 240 may include metal-containing contactplugs 242 that are formed within an interlayer dielectric material 243and which may be connected to respective contact regions of the circuitelements 241. Provided above the device layer 240 may be a firstmetallization layer, which may be represented by a dielectric layer 202and a plurality of metal lines included therein, which are representedby a metal line 203A which extends along, for instance, the transistorwidth direction, i.e., along the horizontal direction in FIG. 2 b.

It should be appreciated that, in advanced semiconductor devicesincluding a plurality of metallization layers, typically the metal linesof one metallization layer are substantially parallel to each other,while the metal lines of an adjacent metallization layer are alsosubstantially parallel but perpendicular to the metal lines of theadjacent metallization layers. It should be appreciated, however, thatthe principles of the present invention are not restricted to anyparticular configuration or orientation of metal lines within a specificmetallization layer.

Above the first metallization layer represented by the dielectric layer202 and the metal line 203A may be a further metallization layer, suchas the metallization layer 230, as illustrated in FIG. 2 a.Consequently, in the first device region 220A, the respective metallines 212A, 212D and 212C may extend substantially perpendicularly tothe metal line 203A and may be formed in an upper portion 205U of adielectric layer 205. Furthermore, the vias 213A may extend through alower portion 205L of the dielectric layer 205 so as to connect arespective metal line with a corresponding metal region or metal line ofa lower-lying metallization layer. In the present example, it may beassumed that the metal line 212A may be connected to the metal line 203Aby means of the via 213A corresponding to the location as specified inFIG. 2 a. It should be noted that the other metal lines 212D, 212C mayalso be connected by respective vias 213A with other metal linescontained in the dielectric layer 202, which, however, may not bevisible in the cross-section of FIG. 2 b.

It should also be appreciated that, ideally, a thickness of the upperportion 205U of the dielectric layer 205 is defined by a thickness ofthe corresponding metal lines 212A, which is, in the design, identicalfor all metal lines and regions. In this respect, it should be notedthat, in some embodiments of advanced semiconductor devices, thedielectric layer 205 may be provided as a substantially continuousdielectric layer, typically comprised of a low-k dielectric material,wherein the finally obtained thickness and thus height of the metallines 212A, 212D and 212C is defined by an etch process. Similarly, inthe second device region 220B, the metal region 212B is provided in theupper portion 205U, wherein, as previously explained, in a real device,the height of the metal region 212B may differ significantly from thecorresponding heights of the metal lines 212A, 212D and 212C due to anyetch non-uniformities when the thickness of the upper portion 205U isdefined by the etch process rather than by any etch stop layers or otherprocess techniques, in which the vias 213A and the metal lines and metalregions in the upper portion 205U are formed in separate processes, aswill be explained in more detail later on. Moreover, the manufacturingsequence for forming the semiconductor device 200 in an actual hardwareconfiguration will be described later on with reference to FIG. 2 d.

On the basis of the semiconductor device 200, i.e., its design layout,as is illustratively depicted in FIGS. 2 a-2 b, specific areas in themetallization layer 230 may be identified in which a reduced via densityis encountered. In one illustrative embodiment, the metal region 212Bmay represent a test structure, for instance for providing process datawith respect to a CMP process with respect to dishing effects and thelike, so that, with respect to any electrical considerations, the region212B may be regarded as a non-functional region, which, however, maysignificantly influence the manufacturing process and also thesubsequent behavior of the device 200, for instance with respect tometal delamination and other defect sources. Due to the non-requiredelectrical function of the region 212B, initially no vias may beprovided below the region 212B. Consequently, the area including themetal region 212B may be identified as an area with reduced via density,wherein a corresponding threshold or other comparison criterion forindicating an area as an area of reduced via density may be establishedon the basis of empirical data, process models and the like. In oneillustrative embodiment, in addition to any electrically non-functionalmetal regions, such as the region 212B, electrically functional regionsmay also be examined with respect to their via density so as to identifya reduced via density. For example, in the embodiment shown, the metalline 212C may be identified as an area of reduced via density, wherein,depending on the configuration of the underlying metallization layer,specific areas may be determined which may be appropriate for receivingadditional dummy vias to enhance the overall performance of the metalline 212C.

After the identification of respective areas with reduced via density,the semiconductor device 200, i.e., its design layout, may bere-designed to include at least some dummy vias in the one or moreidentified regions of reduced via density. In one illustrativeembodiment, the area of the lower portion 205L of the dielectric layer205, located below the metal region 212B, may be identified as acorresponding region of reduced via density and thus the design of thesemiconductor device 200 may be altered to include one or more dummyvias located below the metal region 212B and connected thereto. In stillother embodiments, functional metal regions, such as the metal line212C, may be identified as being located above a region of reduced viadensity, wherein, in this case also, certain areas in the lower portion205L of the dielectric layer 205 may be identified which may beappropriate for receiving additional dummy vias without providingelectrical contact to any lower-lying metallization layers.

FIG. 2 c schematically shows the semiconductor device 200 or itsmodified layout in a top view, wherein at least some additional dummyvias are provided in order to enhance the performance of the respectiveoverlying metal regions. In FIG. 2 c, a plurality of dummy vias 213B areprovided, which are connected to the metal region 212B and which mayterminate in a dielectric material, such as the layer 202 (FIG. 2 b),without affecting the electric functionality of the semiconductor device200. Moreover, in one illustrative embodiment, additional dummy vias213B may also be provided in one or more of the electrically functionalmetal lines, such as the line 212C, wherein a sufficient lateraldistance with respect to any metal lines provided in the dielectriclayer 202, such as the metal line 203A, may be maintained in order toreliably avoid any shortage between the metal line 212C and a lowerlyingmetal line for which no electrical connection is included in theoriginal design of the device 200.

It should be appreciated that, in some illustrative embodiments, thedummy vias 213B may have substantially the same configuration as thefunctional vias 213A, thereby ensuring a high degree of processuniformity during the formation of the vias 213A and the dummy vias213B. In other illustrative embodiments, the dummy vias 213B or aportion thereof may be formed on the basis of different design criteria,thereby providing the potential for specifically enhancing theperformance in combination with the respective overlying metal regions.For example, it may be advantageous to increase the size of the dummyvias 213B and/or alter the distance between adjacent vias in order toenhance the mechanical stability of the dielectric material that remainsbetween the dummy vias 213B. Moreover, the shape of the dummy vias 213Bmay be selected on the basis of mechanical criteria rather than adoptingdesign criteria appropriate for the functional vias 213A. For instance,the cross-section, when viewed in the top view of FIG. 2 c, may have anyappropriate shape, such as circular, polygonal, square, rectangular andthe like.

FIG. 2 d schematically shows a cross-sectional view of the semiconductordevice 200 according to a real implementation on the basis of the device200 as shown in FIG. 2 c, which comprises the additional dummy vias213B. The cross-section of FIG. 2 d may be taken along the lineindicated by IId, similar to the cross-section as shown in FIG. 2 b.

Thus, the semiconductor device 200 as shown in FIG. 2 d comprises thesubstrate 201, which may represent any appropriate substrate havingformed thereon a semiconductor layer suitable for the formation of thecircuit elements 241, such as transistors, capacitors, resistors and thelike. The substrate 201 may represent, in some embodiments, a bulksilicon substrate having formed thereon an appropriate crystallinesemiconductor layer, or, in other embodiments, the substrate 201 mayrepresent an SOI substrate having formed thereon a semiconductor layerseparated from the rest of the substrate by a buried insulating layer,wherein this arrangement may provide enhanced performance in terms ofoperating speed, radiation immunity and the like. It should beappreciated, however, that any other appropriate semiconductor materialsmay be used, wherein, in particular, in sophisticated applications, thesubstrate 201 may have formed therein crystalline regions of differentcrystallographic orientations and/or inherent strain and/or differentmaterial compositions, and the like. The substrate 201 comprises thefirst device region 220A, which may represent a region of the device 200including the plurality of circuit elements 241 and interconnectstructures providing the electrical connections between the individualcircuit elements 241. The second device region 220B may represent aregion that may include circuit elements (not shown) which may not needto be connected by any overlying metallization layer, or the region 220Bmay represent an area of the substrate 201 reserved for test andmeasurement purposes, wherein, as previously explained, the first andthe second device regions 220A, 220B may be provided within the same dieor, in other embodiments, the second device region 220B may be providedat specified locations across the entire substrate 201. Formed in and onthe substrate 201 are the circuit elements 241 and the correspondingcontact plugs 242, thereby forming the device layer 240. In advancedsemiconductor devices, the circuit elements 241 may have a minimumcritical dimension, such as a gate length of field effect transistors,i.e., in FIG. 2 d, a dimension in the direction perpendicular to thedrawing plane of FIG. 2 d, of approximately 50 nm and even less. Thecircuit elements 241 and the respective contact plugs 242 may be formedin the dielectric layer 243, which may be provided as a layer stackincluding dielectric materials, such as silicon nitride, silicondioxide, silicon oxynitride, silicon carbide, nitrogen-enriched siliconcarbide and the like.

The semiconductor device 200 further comprises a first metallizationlayer comprised of the dielectric layer 202 and a plurality of metallines, which are represented by the metal line 203A. As is shown, themetal line 203A may extend across a significant portion of the firstdevice region 220A, while substantially no metal lines are formed in thedielectric layer 202 corresponding to the second device region 220B. Inadvanced semiconductor devices, the layer 202 may comprise a low-kdielectric material, wherein, in some illustrative embodiments, anappropriate low-k material may be hydrogenated silicon oxycarbide(SiCOH), whereas, in other illustrative embodiments, other suitablelow-k polymer material may be used. Formed above the dielectric layer202 and the metal line 203A is the etch stop layer 204, which may becomprised of silicon nitride, silicon carbide, nitrogen-enriched siliconcarbide and the like. Formed above the etch stop layer 204, which alsoacts as a capping layer for the metal line 203A, is the metallizationlayer 230, which may represent, in this illustrative embodiment, thesecond metallization layer. The metallization layer 230 may comprise thedielectric layer 205, which may include the upper layer portion 205U andthe lower portion 205L, wherein the lower portion 205L may be defined bythe vias 213A, 213B extending through the lower portion 205L. Similarly,the upper portion 205U may be defined by the vertical extension of therespective metal lines 212A, 212D, 212C and the metal region 212B. Inthis respect, it should be appreciated that any positional informationand statements, such as “upper,” “lower,” “above,” “below,” “vertical,”“horizontal,” “lateral” and the like may be understood with respect tothe substrate 201. For example, a lateral direction is to be consideredas a direction substantially extending parallel to a surface 201S of thesubstrate 201. A component or layer is located below another layer whenthe distance of the former component or layer with respect to thesurface 201S is less compared to the latter layer.

Contrary to the conventional device as described with reference to FIGS.1 a-1 d, the dummy vias 213B are provided below the metal region 212Band are connected thereto with one end, while the other end of the dummyvias 213B may terminate in the dielectric material of the layer 202. Dueto the provision of the dummy vias 213B, the overall surface of themetal comprising the region 212B and the dummy vias 213B that is incontact with the dielectric material of the layer 205 is significantlyincreased, thereby providing an enhanced adhesion so that a delaminationof the metal region 212B during the formation of the semiconductordevice 200 may be significantly reduced. As previously explained,copper-based metals are typically used in combination with low-kdielectric materials, which per se exhibit a reduced mechanicalstability. Hence, during thermal and mechanical stress encounteredduring the fabrication and/or the operation of the device 200, a reducedadhesion of the copper-based metal to the surrounding dielectricmaterial may result in an increased defect rate, a partial or even totaldelamination of a specified metal region, or any other defectmechanisms. For example, in advanced devices, extremely high currentdensities may be encountered during the operation of the device, whereina reduced adhesion of the metal line to the surrounding dielectricmaterial may also reduce the resistance against electromigration,thereby significantly affecting the overall reliability of the metalline under consideration and thus of the entire semiconductor device200. Even if the metal region 212B is to represent a test area locatedoutside of an actual die region, a reduced adhesion during thesubsequent manufacturing processes may result in a reduced reliabilityof the corresponding metal regions in the first device region 220A,since the reduced mechanical stability during, for instance, a CMPprocess, which may be substantially caused by the reduced adhesion ofthe regions 212B, may also affect adjacent die regions including thefirst device region 220A, thereby also rendering these device regionsless reliable during the subsequent processing and even later on duringthe operation of the finally completed semiconductor device 200, whichmay no longer include the metal region 212B.

A typical process flow for forming the semiconductor device 200 maycomprise substantially the same processes as previously described withreference to the semiconductor device 100. Hence, after the formation ofthe circuit elements 241 within the device layer 240 including thecontact plugs 242 on the basis of well-established recipes, the firstmetallization layer, represented by the dielectric layer 202 and the oneor more metal lines 203A, may be formed on the basis of well-establishedtechniques wherein, as previously explained, a low-k dielectric materialis frequently used in combination with copper or copper alloys.Thereafter, the second metallization layer 230 may be formed byproviding an appropriate dielectric material, such as a low-k dielectricmaterial, wherein, in one illustrative embodiment, corresponding viaopenings may be formed in the upper and lower portions 205U, 205L of thedielectric layer 205 on the basis of the modified layout design as shownin FIG. 2 c. Consequently, a plurality of respective via openings arealso formed at least below an area corresponding to the metal region212B still to be formed. In other embodiments, as previously explained,respective via openings may also be formed in any device areas that mayhave been identified as areas of reduced via density on the basis of theinitial design layout of the device 200 described with reference toFIGS. 2 a-2 b.

Thereafter, by well-established techniques, corresponding openings forthe metal lines 212A, 212D, 212C and the metal region 212B may be formedabove the corresponding via openings including openings for thefunctional vias 213A and the dummy vias 213B. As previously noted,during the corresponding anisotropic etch process for forming therespective openings, a significantly increased process uniformity may beachieved, since similar etch conditions may be established for formingthe opening for the region 212B and for the formation of the trenchopenings corresponding to the regions 212A, 212D, 212C. As aconsequence, the respective openings for the regions 212A, 212D, 212Cand 212B may be formed with substantially a similar depth in the upperlayer portion 205U so that, in general, a more uniform and enhancedmetal thickness may be obtained in the metallization layer 230.Thereafter, the corresponding openings may be filled with appropriatebarrier and seed layers followed by the deposition of the actual metalin a common manufacturing process.

In further illustrative embodiments, the respective openings for themetal lines 212A, 212D, 212C and for the metal region 212B may be formedfirst in the upper portion of dielectric layer 205 and thereafter thecorresponding via openings for the vias 213A, 213B may be formed. Evenin this case, an enhanced reliability of the resulting metal region 212Bmay be achieved, since even after any etch non-uniformities may haveoccurred, which may result in a reduced depth of the openingcorresponding to the metal region 212B, the dummy vias 213B maynevertheless provide enhanced adhesion of the region 212B, therebysignificantly reducing the risk for any metal delamination in subsequentprocesses.

FIG. 2 e schematically shows the semiconductor device 200 according toanother illustrative embodiment, wherein the vias 213A and the dummyvias 213B are completely formed prior to the formation of thecorresponding metal lines and metal regions. For this purpose, the lowerportion 205L may be formed and may be subsequently patterned to receivecorresponding via openings in accordance with the design of thesemiconductor device 200 as shown in FIG. 2 c. Thereafter, therespective openings may be coated with appropriate barrier and seedmaterials and thereafter the actual metal, such as copper, may bedeposited on the basis of well-established techniques. Next, any excessmaterial may be removed, for instance by CMP and/or electrochemical etchtechniques. Thereafter, the upper portion 205U may be formed, possiblyby providing an intermediate etch stop layer, and may then be patternedto provide the corresponding openings for the metal lines 212A, 212D,212C and the metal region 212B, which are then filled with barriermaterial and the actual metal. As a result, an enhanced reliability forthe metal region 202B may also be obtained for the device 200 asfabricated according to FIG. 2 e.

FIG. 3 schematically shows a cross-sectional view of a semiconductordevice 300 in accordance with yet another illustrative embodiment of thepresent invention. The semiconductor device 300 may comprisesubstantially the same components as the semiconductor device 200.Hence, the device 300 may comprise a substrate 301 on which is formed adevice layer 340 including a plurality of circuit elements 341, such asfield effect transistors, which may have, for instance, a minimalcritical dimension 341A of 50 nm or even less. The device layer 340 mayfurther comprise corresponding contact plugs 342 which may be connectedto respective metal lines 303A formed in a dielectric layer 302.Contrary to the previously described embodiments, the device 300 maycomprise, in a second device region 320B, one or more dummy metalregions 303B, which may comprise, together with the metals lines 303Aand the dielectric layer 302, the first metallization layer of thedevice 300. In other embodiments, the metal lines 303A and the dummymetal regions 303B may be part of a higher metallization layer so thatthe metal lines 303A may not be directly in contact with the respectivecontact plugs 342. Moreover, a further metallization layer 330, in theillustrated embodiment the second metallization layer, is formed toinclude a plurality of functional vias 313A connecting to respectivemetal lines 303A, while a plurality of dummy vias 313B may be provided,wherein at least some of the dummy vias 313B may connect to a respectivedummy metal region 303B. Moreover, corresponding metal lines 312A may beformed in the first device region 320A, while a metal region 312B, suchas a large-area test region and the like, may be formed above the dummyvias 313B.

Regarding the process flow for forming the semiconductor device 300, thesame criteria apply as previously explained with reference to thesemiconductor devices 100 and 200. It should be appreciated, however,that a corresponding design of the semiconductor device 300 is alteredwith respect to the design of the semiconductor device 200 so as to nowobtain the dummy metal regions 303B in any appropriate size and shape.For example, the dummy metal regions 303B may represent metal linesextending substantially parallel to the metal lines 303A, whereas, inother embodiments, the dummy metal regions 303B may represent metalislands on which one or more dummy vias 303B terminate. The dummy metalregions 303B are electrically non-functional in the sense that thesedummy metal regions 303B may not provide an electrical contact to any ofthe circuit elements 341. It should be appreciated, however, that aplurality of corresponding dummy metal regions 303B may be provided inother adjacent metallization layers, wherein at least the very firstdummy metal region, i.e., the dummy metal region located closest to thesubstrate 301, may not be electrically connected to respective circuitelements 341. Due to the provision of the dummy metal regions 303B,which act as “anchors” for the dummy vias 313B and thus for thecorresponding metal regions 312B, the mechanical stability of themetallization layer 330 may be even more enhanced.

As a result, the present invention provides a new technique for theformation of metallization layers including electrically non-functionalmetal regions, the mechanical stability of which may be significantlyenhanced by forming one or more dummy vias below the corresponding metalregions. Moreover, by identifying device areas with reduced via densityand by correspondingly re-designing the semiconductor device underconsideration, an enhanced process uniformity may be achieved, therebyalso contributing to an overall performance gain and/or to an enhancedproduction yield. Furthermore, the provision of dummy vias may not berestricted to electrically non-functional metal regions but may also beapplied to metal lines and other metal regions, thereby also enhancingthe electrical as well as mechanical performance of these functionalmetal lines and regions. For example, by providing any dummy vias for ametal line, the overall resistance thereof may be reduced and at thesame time the mechanical stability thereof may be significantlyenhanced.

The particular embodiments disclosed above are illustrative only, as theinvention may be modified and practiced in different but equivalentmanners apparent to those skilled in the art having the benefit of theteachings herein. For example, the process steps set forth above may beperformed in a different order. Furthermore, no limitations are intendedto the details of construction or design herein shown, other than asdescribed in the claims below. It is therefore evident that theparticular embodiments disclosed above may be altered or modified andall such variations are considered within the scope and spirit of theinvention. Accordingly, the protection sought herein is as set forth inthe claims below.

1. A method, comprising: identifying a region of reduced via density ina metallization layer of a semiconductor device by determining an areain said metallization layer for receiving a metal region therein on thebasis of design rules for said semiconductor device, determining anumber of functional vias located below said metal region and connectedthereto and obtaining a measure for a density of said functional vias onthe basis of design values relating to said metal region and saidfunctional vias, wherein the region is identified based on said measure;forming a dummy via in said identified region beneath said metal region;and forming the metal region above said identified region, said metalregion connecting to said dummy via.
 2. The method of claim 1, whereinidentifying said region of reduced via density further comprisescomparing said measure with a reference criterion and re designingdesign rules for said semiconductor device to include at least one dummyvia located below said metal region when a result of said comparingindicates a reduced via density.
 3. The method of claim 1, wherein saiddummy via has substantially the same design dimensions as a functionalvia to be formed in said metallization layer.
 4. The method of claim 1,wherein forming said dummy via and said metal region comprises: forminga dielectric layer above a substrate; forming a via opening in saiddielectric layer; forming an opening above said via opening in saiddielectric layer; and commonly filling said via opening and said openingwith a metal.
 5. The method of claim 1, wherein forming said dummy viaand said metal region comprises: forming a first dielectric layer abovea substrate; forming said dummy via in said first dielectric layer;forming a second dielectric layer above said first dielectric layerincluding said dummy via; and forming said metal region in said seconddielectric layer.
 6. The method of claim 1, wherein forming said dummyvia and said metal region comprises: forming a dielectric layer above asubstrate; forming an opening corresponding to said metal region in saiddielectric layer; forming a via opening in said opening; and commonlyfilling said opening and said via opening with a metal.
 7. The method ofclaim 1, wherein said metal region represents a test region.
 8. Themethod of claim 7, wherein said metal region represents a metal linehaving at least one functional via connected thereto so as to establishan electric connection to at least one circuit element.